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Not thrilled with CL-60 inrush limiter in USA/160W Class A First Watt designs
Not thrilled with CL-60 inrush limiter in USA/160W Class A First Watt designs
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Old 3rd November 2018, 08:06 PM   #1
Mark Johnson is offline Mark Johnson  United States
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Not thrilled with CL-60 inrush limiter in USA/160W Class A First Watt designs
Default Not thrilled with CL-60 inrush limiter in USA/160W Class A First Watt designs

I've got my First Watt M2x amplifier doing a Thermal Soak right now. M2x is a Class A amplifier that draws 160 watts from the AC mains. With USA voltage that means about 1.4 amps average mains current.

This amp has two Amphenol CL-60 inrush current limiters, connected in parallel for USA: each ICL feeds one of the two parallel primary windings on the power transformer. Thus each CL-60 sees about 0.7 amps average current. But, checking its datasheet, the CL-60 is designed to run at (1.2A <= Current <= 5.0A). Uh oh.

General Electric / Thermometrics / Amphenol don't specify the ICL body temperature on their datasheets, but other companies do. I've attached a representative one below. It runs at 149 degrees Celsius! wow.

I just measured the CL-60 ICLs in my M2x. After three hours of thermal soaking (power applied, inputs shorted), the body of the CL-60's measure 33.8 degrees Celsius using a Type-K thermocouple, and 32.9 degrees Celsius using an infrared no-contact thermometer. That's a far cry from 149 C. So I'm thinking the CL-60 may not be the best ICL for this particular amplifier.

Poking around on Mouser's website, I found the SL15-22102 Inrush Current Limiter from Antherm. Its cold resistance is 22X higher than the CL-60's cold resistance, so it gives a whole lot more protection against inrush. Its max energy rating is 40 Joules, slightly higher than the CL-60's rating of 36 Joules. Its resistance at 0.7 amps of average current is about 2.5 ohms, so the mains voltage "lost" to ICL is 1.75 volts, which is about 1.5% of the total mains voltage. I find this acceptable. I think I'll order a few of these and play around with them. Perhaps the best choice is something sort of in-between this one, and the CL-60 original.

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Old 3rd November 2018, 09:38 PM   #2
jean-paul is offline jean-paul  Netherlands
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Hi, do you mean that you rather would like to see the CL-60 at 149 degrees Celsius instead of 33 degrees Celsius?
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Old 3rd November 2018, 09:44 PM   #3
gl is offline gl  United States
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Hi Mark,

I’m curious. Why not use use just one CL-60 and then parallel the primary’s? That gets you over the 1.2 amp threshold stated on the data sheet.

Graeme
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Old 3rd November 2018, 09:57 PM   #4
CharlieLaub is offline CharlieLaub  United States
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I believe that you are never supposed to use NTC thermistors in parallel.
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Old 3rd November 2018, 09:57 PM   #5
Mark Johnson is offline Mark Johnson  United States
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Not thrilled with CL-60 inrush limiter in USA/160W Class A First Watt designs
Quote:
Originally Posted by jean-paul View Post
Hi, do you mean that you rather would like to see the CL-60 at 149 degrees Celsius instead of 33 degrees Celsius?
I would prefer to see two CL-90s or CL-120s at 149 degrees Celsius instead of two CL-60s at 33 degrees Celsius.

However I like the other ICLs mentioned above, not made by Amphenol and with a part number that does not begin CL-. They appear to me to be even better suited than CL-90, to the M2x with USA voltages.
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Old 3rd November 2018, 10:08 PM   #6
Mark Johnson is offline Mark Johnson  United States
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Not thrilled with CL-60 inrush limiter in USA/160W Class A First Watt designs
Here's the existing PCB. It's got two CL60s; I'm using the USA mains option. If you decide the two CL60s are not really in parallel, it's just that each one carries half the primary current, that's okay with me.

I prefer to drop new parts into the existing PCB rather than bodge in a different circuit topology. Modification laziness.

I also kind of like Nelson Pass's idea of getting double the max inrush energy capability, by having two $1.00 ICLs working in parallel, instead of just one.

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Old 3rd November 2018, 10:16 PM   #7
jean-paul is offline jean-paul  Netherlands
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Quote:
Originally Posted by Mark Johnson View Post
I would prefer to see two CL-90s or CL-120s at 149 degrees Celsius instead of two CL-60s at 33 degrees Celsius.

However I like the other ICLs mentioned above, not made by Amphenol and with a part number that does not begin CL-. They appear to me to be even better suited than CL-90, to the M2x with USA voltages.
They only will reach maximum temp at startup and not after some time when they enter steady state current. Or am I thinking wrong? Inrush current limters only get hot for a short time.
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Old 3rd November 2018, 10:22 PM   #8
juanitox is offline juanitox  France
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inrush limiter are for sissies , i don't use them in my power supply , i just use bigger bridge rectifier
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Old 3rd November 2018, 11:37 PM   #9
moe29 is offline moe29  United States
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i've used them in my Aleph 2 clones for over 15 years and they've been just fine...
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Old 4th November 2018, 01:03 AM   #10
wayne is offline wayne  United States
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Not thrilled with CL-60 inrush limiter in USA/160W Class A First Watt designs
The Amatherms are a good product they have a broad range and go up to about 750 joules if my memory is correct. They should run toasty to get the resistance down and have minimal loss. They will current hog in parallel but not an issue with dual primary windings.
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